1. Technical Field
The invention relates to a polymerizable compound having two polymerizable groups, wherein one is bonded directly to the ring and the other is bonded to the ring through a spacer (a bonding group), a composition including the polymerizable compound, a polymer obtained from the composition, and their use.
2. Technical Background
A liquid crystal display device typified by a liquid crystal display panel, a liquid crystal display module and so forth utilizes optical anisotropy, dielectric anisotropy and so forth, those of which are possessed by a liquid crystal compound. An operating mode of this liquid crystal display device includes a PC (phase change) mode, a TN (twisted nematic) mode, a STN (super twisted nematic) mode, a BTN (bistable twisted nematic) mode, an ECB (electrically controlled birefringence) mode, an OCB (optically compensated bend) mode, an IPS (in-plane switching) mode, a FFS (fringe field switching) mode and a VA (vertical alignment) mode.
A liquid crystal display device containing a liquid crystal composition to which a polymerizable compound is added is also known. In a liquid crystal display device having a PSA (polymer sustained alignment) mode, for example, a small amount of a polymerizable compound (for example, approximately 0.3% by weight to approximately 1% by weight) is added to a liquid crystal composition, which is then introduced to a liquid crystal display cell. The cell is irradiated usually with ultraviolet light under the conditions of applied voltage between the electrodes, polymerizing the polymerizable compound and forming a polymer structure in the cell. A liquid crystal display device having an improved screen burn-in and a decreased response time is obtained by this method.
This method is applied to a variety of liquid crystal display devices, and modes such as PS-TN, PS-IPS, PS-FFS, PSA-VA and PSA-OCB are known. A polymerizable compound that is added to a liquid crystal composition for use in the devices having these modes has a rigid structure. It is said that the compound generally has a high ability for orienting liquid crystal molecules. On the other hand, the compound has a poor solubility in the liquid crystal composition and a large amount of the polymerizable compound cannot be added (Patent document No. 1 to Patent document No. 5).